In a wireless network a radio receiver is a function in a radio node for receiving radio transmissions from one or multiple radio transmitters. One of the most important and most fundamental problems in a wireless network is to set the output power of the radio transmitters. In many wireless networks, for example a Long-Term Evolution, LTE, network, the radio links have a downlink, DL, and an uplink, UL, where a DL is a transmission from an enhanced NodeB, eNB, that also schedules the radio link and a UL is a transmission from a User Equipment, UE, scheduled from an eNB.
Typically, an eNB uses a determined output power in both UL and DL radio links from and to a UK The DL-power has often a fixed power spectral density according to the maximal power. The UL-power is then determined by that the eNB transmits a DL reference signal that the UEs measure and adapt their output power in order to make the received power of all UL transmissions to be more or less the same at the eNB. Sometimes, an eNB allows for adjustment for e.g. measurement errors in which the eNB transmits so called transmit power control, TPC, commands to UEs to adjust the power.
In LTE, power control is applied for uplink physical channels. The aim for the power control is to maintain a target received power at the receiving base station (Enhanced NodeB, eNB). For the uplink data channel, Physical Uplink Shared Channel, PUSCH, the transmitted power by a User Equipment, UE, in a subframe i is determined by the formula:PPUSCH(i)=min{PCMAX,10 log10(MPUSCH(i))+PO_PUSCH(j)+α(j)·PL+ΔTF(i)+f(i)}PCMAX(i) is the configured maximum UE transmit power, MPUSCH(i) is the number of resource blocks allocated for the UE, PO_PUSCH(j) is a parameter consisting of the sum of a cell-specific and a UE-specific part provided by higher layers, α is cell-specific parameter configured by higher layers (also known as fractional path loss compensation factor), PL is the UL path loss estimate calculated in the UE, ΔTF(i) is a UE-specific parameter provided by higher layers and f (i) is a UE-specific correction term controlled by transmit power control, TPC, commands sent in UL grants sent on the Physical Downlink. Control Channel, PDCCH. For later releases of the Third Generation Partnership Project, 3GPP, specifications the power control is slightly more complicated due to the support of multi-carrier where a UE can support multiple serving cells.
Technical Specifications, TS, for power control are described in versions of 3GPP TS36.331, “Evolved Universal Terrestrial Radio Access (E-UTRA); Radio Resource Control (RRC) protocol specification”. Power control arrangements of the type outlined above may be found in versions under Release 11 and higher.